Correct Answer: B

Rationale: The correct answer is B. Femur. The femur, also known as the thigh bone, is located in the human thigh. It is the longest and strongest bone in the human body, extending from the hip to the knee. The ulna, radius, and humerus, on the other hand, are bones found in the arm. Therefore, choices A, C, and D are incorrect as they are bones of the arm, not the thigh.

Correct Answer: D

Rationale: The term 'lateral' refers to the direction away from the midline of the body. In this case, the cheekbones are situated to the sides of the nose, making them lateral to the nose. Therefore, 'lateral' correctly describes the position of the cheekbones in relation to the nose. Choices A, B, and C are incorrect: A. 'Anterior' means situated at or towards the front, which is not the correct description of the cheekbones in relation to the nose. B. 'Proximal' means situated nearer to the center of the body, which is not the correct description of the cheekbones' position in relation to the nose. C. 'Deep' refers to being situated further away from the surface, which is not the appropriate term to describe the cheekbones' position in relation to the nose.

Correct Answer: D

Rationale: The correct answer is D. Parathyroid hormone plays a crucial role in activating vitamin D. This activation occurs in the kidneys, where parathyroid hormone stimulates the conversion of inactive vitamin D to its active form. Active vitamin D is essential for maintaining proper levels of calcium and phosphorus in the body, which are important for bone health and other physiological functions. Choices A, B, and C are incorrect because parathyroid hormone is not involved in increasing energy levels, stimulating cell reproduction, or speeding up metabolism. Its primary function is related to calcium and phosphorus homeostasis through the activation of vitamin D.

Correct Answer: B

Rationale: The esophagus is part of the digestive system. It is a muscular tube that connects the mouth to the stomach, allowing the passage of food and liquids from the mouth to the stomach for digestion. The esophagus plays a crucial role in the process of swallowing and digestion, which are essential functions of the digestive system. Choices A, C, and D are incorrect because the esophagus is not associated with the endocrine, respiratory, or nervous systems.

Correct Answer: C

Rationale: Calciferol, commonly known as Vitamin D, is regulated by the parathyroid gland, not the thyroid, pituitary, or hypothalamus. The parathyroid gland plays a crucial role in maintaining calcium and phosphorus balance in the body by regulating the production of calcitriol, the active form of Vitamin D. This hormone helps in the absorption of calcium from the intestines and its reabsorption in the kidneys to maintain proper calcium levels in the blood. Therefore, the correct answer is the Parathyroid gland (Choice C). Choices A, B, and D are incorrect as they do not have a direct role in controlling Calciferol.